The present invention relates to mounting and connection devices for use with microelectronic elements such as semiconductor chips.
Complex microelectronic devices such as modern semiconductor chips require numerous connections to other electronic components. For example, a complex microprocessor chip may require hundreds of connections to external devices.
Semiconductor chips have commonly been connected to electrical traces on mounting substrates using several alternative methods, including wire bonding, tape automated bonding and flip-chip bonding. Each of these techniques presents various problems including difficulty in testing the chip after bonding, long lead lengths, large areas occupied by the chip on the microelectronic assembly, and fatigue of the connections due to changes in the sizes of the chip and the substrate under thermal expansion and contraction.
Structures that have been used to successfully address the foregoing problems are disclosed in commonly assigned U.S. Pat. Nos. 5,148,265; 5,148,266; and 5,455,390. Structures according to the embodiments taught in these patents comprise a flexible, sheet-like element having a plurality of terminals disposed thereon. Flexible leads are used to connect the terminals with contacts on a first microelectronic element such as an integrated circuit. The terminals may then be used to test the microelectronic chip, and may be subsequently bonded to a second microelectronic element. The flexible leads permit thermal expansion of various components without inducing stresses in the connection.
Commonly assigned U.S. Pat. No. 5,518,964 (xe2x80x9cthe ""964 patentxe2x80x9d), hereby incorporated in its entirety herein, discloses further improvements in microelectronic connections. In certain embodiments of the ""964 patent, a flexible, sheet-like element has a first surface with a plurality of elongated, flexible leads extending from a terminal end attached to the sheet-like element to a tip end offset from the terminal end in a preselected, first horizontal direction parallel to the sheet-like element. The tip ends have bond pads for connection to a microelectronic element. As the term is used herein, xe2x80x9cmicroelectronic elementxe2x80x9d encompasses circuit boards, integrated circuits, connection components such as polyimide or other dielectric sheets, and other components used in microelectronic circuitry. Each of the plurality of leads is simultaneously formed by moving all of the tip ends of the leads relative to the terminal ends thereof so as to bend the tip ends away from the sheet-like element. This is accomplished by relative movement between the sheet-like element and the microelectronic element.
The tip ends of the leads are initially attached to the sheet-like element. The initial position of the bond pad on the tip ends is thereby fixed with respect to the terminal ends in order to facilitate attachment to the microelectronic element.
Various lead configurations are disclosed in the ""964 patent. In one such configuration, the leads comprise straight, elongated bodies of conductive material extending between terminal ends connected to a dielectric sheet-like element and tip ends to be connected to a microelectronic element. The terminal end of the lead is attached through a via in the sheet-like element to another microelectronic element on the other side of the sheet-like element.
The attachment of the tip ends of the leads to the sheet-like element is releasable. After bonding the tip ends to the microelectronic element, the leads are formed in their final configuration by moving the sheet-like element and the microelectronic elements relative to each other in two directions: in a vertical direction away from each other, and in a horizontal direction parallel to the sheet-like element. As a result, the tip end of the lead is separated from the sheet-like element and traces an arcuate path relative to the other end of the lead. That movement prevents stretching of the lead during formation and results in an S-shaped configuration of the lead that is advantageous in absorbing further relative movement between the sheet-like element and the microelectronic element due to thermal expansion/contraction during operation of the resulting device.
In another lead configuration taught in the ""964 patent, the lead is initially a curved strip disposed on a surface of the sheet-like element. A terminal end of the lead is connected to a terminal through a via in the sheet-like element and a tip end is bonded to a microelectronic element. In forming those leads to a final configuration, the sheet-like element and the microelectronic element are moved away from each other in a vertical direction only. The curve of the lead is partially straightened by the relative movement of the elements. The xe2x80x9cslackxe2x80x9d created by the initial curve in the lead permits vertical displacement of the microelectronic components without the necessity of providing additional lead length by horizontally displacing the components.
A number of such configurations of curved leads are disclosed in the ""964 patent. An S-shaped lead structure permits nesting of adjacent leads in configurations requiring a high lead density. A U-shaped lead configuration permits a larger relative displacement of the microelectronic components in a vertical direction without a corresponding horizontal displacement. Numerous other lead configurations are contemplated in the ""964 patent.
Still further improvement in the above-described configurations and processes would be desirable.
One aspect of the present invention provides a microelectronic lead element for connecting first and second microelectronic elements. The lead element comprises a body section and two strip-like flexible leg sections. Each leg section has a base end connected to the body section and a tip end offset from the body section in a horizontal offset direction. Each tip end is attached to a corresponding one of the two microelectronic elements. The leg sections are substantially parallel to one another so that movement of one of the tip ends with respect to the other in a vertical direction perpendicular to the horizontal offset direction causes flexure of the leg sections in opposite directions relative to the rigid body.
The tip ends may have bonding material thereon facing in opposite vertical directions. The body may be rigid and may have a thickness greater than or the same as the thickness of the leg sections, and the leg sections and the body section may be gold, copper, nickel or similar materials or composites thereof.
A microelectronic assembly is formed by a plurality of such lead elements connecting first and second microelectronic elements having horizontal surfaces facing one another. One tip end of each lead element is connected to one of the microelectronic elements, and a second tip end is connected to the other microelectronic element so that the lead elements electrically interconnect the microelectronic elements. A dielectric sheet may overlie a surface of one of the microelectronic elements, with the rigid body and leg sections of the lead elements have coplanar surfaces releasably attached to the dielectric sheet. The dielectric sheet has a via proximate to one of the tip ends for connection of that tip end to one of the microelectronic elements.
The microelectronic assembly may be processed by moving the first and second microelectronic elements away from one another in a vertical direction to bend the leg sections of the lead elements.
In another aspect of the invention, a microelectronic assembly has first and second microelectronic elements with horizontal surfaces facing one another, and a plurality of lead elements disposed between those surfaces. Each lead element includes two elongated, flexible leads, each lead having a terminal end connected to a horizontal surface of the corresponding microelectronic element, and a tip end movable away from that microelectronic element and offset from the terminal end in a horizontal direction, also referred to herein as the xe2x80x9coffset direction.xe2x80x9d The tip ends of the two flexible leads are in registry and are connected. The terminal ends of the two leads in each of the lead elements may be aligned with one another. Upon movement of the microelectronic elements away from one another, the lead elements deform. The connected tip ends of the leads are pulled away from the microelectronic elements, and may lie approximately midway between the microelectronic elements in the finished assembly.
The offset directions of the two lead elements may be the same. Further, offset directions of different ones of the lead elements may be different from one another. In that case, there may be a substantially equal number of lead elements having opposite offset directions.
The assembly may further comprise a first dielectric sheet overlying the facing surface of the first microelectronic element; a similar dielectric sheet may overlie the facing surface of the second microelectronic element. The leads are releasably attached to the dielectric sheets, and the dielectric sheets have vias near the terminal ends of the leads for connection of the leads to the microelectronic elements.
In another embodiment of the invention, a connector element for connecting first and second microelectronic elements comprises a dielectric sheet with first and second primary surfaces and a plurality of lead elements. Each of those lead elements includes a first elongated, flexible lead overlying the first surface of the dielectric element, and has a terminal end and a tip end offset from the terminal end in a first offset direction. Each lead element also has a second, elongated, flexible lead overlying the second surface of the dielectric sheet. The second lead has a terminal end connected to the terminal end of the first lead and a tip end offset from the terminal end of the second lead in a second offset direction. The tip ends of both leads are releasably attached to the surfaces of the dielectric sheet.
Within each lead element, the terminal ends of the first and second leads may be aligned with one another. Further, a plurality of vias may extend between the primary surfaces of the dielectric sheet, and at least some of the lead elements may have terminal ends of their first and second leads connected to one another through the vias.
Within each lead element, the first and second offset directions may be the same. Furthermore, the first and second offset directions of all the lead elements may be the same. In addition, the amount of offset between the tip ends and the terminal ends in all of the lead elements may be the same.
On at least some of the leads, there may be bonding material on the tip ends facing away from the surface of the dielectric sheet that lead is overlying. The tip ends of the first and second leads in each of the lead elements may be aligned with one another.
In another aspect of the invention, a microelectronic assembly comprises such a connector element in combination with first and second microelectronic elements with horizontal surfaces facing one another. The connector element is disposed between the mutually facing surfaces of the microelectronic elements. The tip end of the first lead of each of the lead elements is connected to the first microelectronic element, and the tip end of the second lead of each of the lead elements is connected to the second microelectronic element. The lead elements thus electrically interconnect the microelectronic elements.
In a method of processing such a microelectronic assembly, the first and second microelectronic elements are moved away from one another in a vertical direction to bend the lead elements and displace the dielectric sheet in a horizontal direction.
These and other objects, features and advantages to the present invention will be more readily apparent from the detailed description of the preferred embodiments set forth below, taken in conjunction with the accompanying drawings.